The objectives of the study are to continue the ongoing Phase III randomized polycythemia vera study and the associated "efficacy" studies. By means of the major PVSG protocol the therapy amongst phlebotomy, radioactive phosphorus and chorambucil will be selected as being optimum resulting in the least morbidity and the longest survival. The natural history of polycythemia vera will be characterized and the modifying effects of myelo-suppressive therapy determined. Cytogenetic abnormalities are being detected by studies of the bone marrow and histopathologic marrow examinations are being performed.